1. Field of the Invention
This invention relates in general to semiconductor devices and, more particularly, to a semiconductor device assembly having a integral heat sink.
2. Description of the Related Art
As used herein, the term "semiconductor chip" refers to a silicon chip or die containing circuitry to form an active device. The term "semiconductor device assembly" refers to the semiconductor chip and associated components. The "associated components" include the leads for connecting the chip to a circuit board, a heat sink for dissipating heat, and an encapsulating package. Efforts to provide better semiconductor device assemblies have targeted the associated components, e.g., the packaging and heat sinks.
To reduce costs and to promote miniaturization, some semiconductor manufacturers are employing a vertical surface mount package (VSMP) having multiple pins. The VSMP package mounts vertically on a circuit board thereby allowing for a greater density of device assemblies without departing from the use of plastic molding materials.
FIG. 1 illustrates a VSMP assembly 1 having a plastic housing 4. The plastic housing 4 is a rectangular parallelepiped having length "a," width "b," and height "c." The width "b" is ordinarily relatively small, e.g., 1.2 mm, compared to the length "a" and the height c. Supports legs 3 provide for vertically mounting the VSMP assembly 1 on a circuit board (not shown).
FIG. 2A is a cross-sectional view of VSMP assembly 1 along line B--B of FIG. 1. Metallic wires 7 connect a semiconductor chip 6 to lead terminals 2 The lead terminals 2 carry input and output signals to and from the semiconductor chip 6.
VSMP assemblies currently house low power semiconductor chips. It would be advantageous to use the VSMP assemblies with semiconductor chips having high power consumption. High power chips include, but are not limited to, static or dynamic random-access memories ("SRAM" or "DRAM", respectively), transistor-transistor logic ("TTL") and Sync-Link DRAM ("SLDRAM"). Power consumption can reach 2 watts in some contemporary high power chips, e.g., current SLDRAM's.
High power semiconductor devices can generate enough the heat to damage a semiconductor chip. Furthermore, the plastic housing impedes heat dissipation due to plastic's insulating properties. For high power chips, the semiconductor device assembly needs elements to dissipate heat that is not efficiently dissipated through the plastic housing.
The prior art has employed heat sinks to dissipate heat generated by high power semiconductor chips. Typically, high power chips are packaged in leadless chip carriers or in quad-flat packages. These types of packages have generally used either internal heat sinks or external heat sinks.
In the internal form, the heat sink is inside the plastic package and in close contact with a large portion of the surface of the chip. The close contact conducts heat from the chip to the heat sink. Nevertheless, since the plastic package is not a good thermal conductor, an internal heat sink does not efficiently transfer heat from the heat sink to the exterior of the package. If an internal heat sink is employed, a high-power semiconductor chip can still overheat.
FIG. 2B illustrates a device assembly 5 employing an external heat sink 8. The heat sink 5 makes mechanical and thermal contact with a support member 9 attached to a back face of the semiconductor chip 6. A portion of the external heat sink 8 makes direct contact with the support member 9 through a hole 11 in a front or large-area surface of the device assembly 5.
Still referring to FIG. 2B, external heats have several drawbacks. First, the hole 11 through a large area surface of the housing can weaken the physical strength of the device assembly 5. Second, attaching the heat 8 sink through the hole 11 does not provide a strong bond. The heat sink 8 may move reducing the quality of the thermal contact between the heat sink 8 and the underlying semiconductor chip 6. Attaching the heat sink 8 flat against the plastic housing 4 can reduce risk of relative motion between the heat sink 8 and the housing 4, but the thermal efficiency for heat dissipation will also be reduced. The external heat sink may not provide an adequate solution to the need for heat dissipation in high power semiconductor chips.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.